1. Division of Global Public Health, Department of Medicine, University of California, San Diego, la Jolla, CA, USA
2. Centro Ambulatorio de Prevención y Atención en SIDA e ITS (CAPASITS), Secretaria de Servicios de Salud del Estado de Baja California, México
3. Department of Medicine, Division of Global Public Health and Department of Pediatrics, Division of Child Development and Community Health, University of California, San Diego, La Jolla, CA, USA